[Joz]

Here are Grant Lewi's interpretations, from 'Heaven Knows What'. Very insightful, and he picks up on qualities that many interpretations miss.
(Also Stephen Arroyo has a pretty spot on analysis of Mars/Neptune contacts)

Mars Conjunct Neptune:
The most powerful magnetic aspect in the horoscope. You have poise, charm, ability, power over people - and a determination to get ahead in the world that rarely fails to succeed. Your aims are definite, and your physical, mental, and intuitive powers work in unison to help you. You have a superstitious belief in many things including your own powers, and something of the magician hovers about you. Doors open at your word, men obey you, and the good things of the world come to you...

Mars Square Neptune:
This aspect accompanies spiritual thought and spiritual leadership and is found in the executives of the Church and of spiritual and occult organizations as well as occasionally among great military leaders who have an unusually magnetic personal hold over their men. It gives you a spiritual insight into the affairs of earth, and a practical viewpoint about ideas of heaven. You are conscious of the two worlds which are not separate entities to you but related and integrated parts of the same whole...

[deleted overly-long quotes against forum rules - Moderator]